A photocatalyst is a substance that absorbs light of a predetermined wavelength band to assist in causing a chemical reaction to take place. For example, a photocatalyst completely oxidizes a toxic substance to carbon dioxide and water using an oxidizing agent (e.g., oxygen or water) under light irradiation.
Since the late 1980's, considerable research has been concentrated on photocatalytic oxidation reactions utilizing photocatalysts as advanced oxidation processes in developed countries. In a typical photocatalytic oxidation reaction, hydroxyl radicals and superoxides are created as intermediates to oxidize organic pollutants. A major advantage of photocatalytic oxidation reactions is that only oxygen can be supplied to sufficiently decompose organic pollutants without the addition of an additional oxidant, such as hydrogen peroxide or ozone, and sterilizing effects can be attained.
Photocatalysts are widely used for the purpose of decomposing pollutants in various industrial fields. In Japan, numerous photocatalytic products capable of decomposing a variety of harmful organic substances are currently being developed and commercialized. For example, photocatalysts are applied to concrete and building exterior materials (e.g., tiles) to maintain the concrete and building surfaces clean for at least ten years. Conventional photocatalytic products are very effective in decomposing organic pollutants but do not sufficiently exert their peculiar performance under conditions protected from light, particularly in a UV-deficient environment, such as indoor. Accordingly, when conventional photocatalytic products are applied to interior products, the performance of the photocatalytic products is greatly reduced.
Korean Patent Application No. 10-2000-0059193 A (Oct. 9, 2000) discloses a packing material for a cooling tower that uses a sterilizing photocatalyst to achieve semi-permanent sterilizing effects, thus eliminating the need for the periodic addition and management of sterilizing agents without causing pollution of cooling water and adversely affecting the equipment.
Korean Patent Application No. 10-2000-0045311 A (Aug. 4, 2000) discloses a water purification system that uses a rotary member having a film coated with titanium oxide as a photocatalyst.
Korean Patent Application No. 10-2000-0035845 A (Jun. 28, 2000) discloses a water purification pot that uses UV light and titanium dioxide as a photocatalyst to purify water in the pot.
Japanese Unexamined Patent Publication No. 2008-105905 (May 8, 2008) discloses a water photolysis system using a photocatalyst.
Japanese Unexamined Patent Publication No. 2008-094709 (Apr. 24, 2008) discloses a photocatalytic mortar admixture for a building that is capable of purifying organic substances.
U.S Patent Publication No. 2007-0297973 (Dec. 27, 2007) discloses a method for preparing a photocatalyst.
U.S Patent Publication No. 2006-0159598 (Jul. 20, 2006) discloses an air purifier using a photocatalyst.